1. Field of the Invention
The present invention relates to a zirconium-based catalyst precursor activated with an activator (also known as a cocatalyst) comprising a mixture of two compounds, to the resulting catalyst composition, and to the use thereof in a process of polymerizing and copolymerizing olefins, especially alpha-olefins.
2. Description of Related Art
Bacskai in U.S. Pat. No. 4,820,786 describes the use of a cocatalyst comprising a mixture of dialkylaluminum halide and dialkyl magnesium to activate a solid supported titanium tetrahalide complex. The activated complex is used to prepare linear low density polyethylene by the copolymerization of ethylene and 1-butene.
It is also known that certain zirconium complexes containing pi-bonded organic ligands, such as bis(cyclopentadienyl)zirconium complexes, activated with an aluminum compound of the aluminoxane type produce olefin polymers and copolymers, such as ethylene and propylene homopolymers, ethylene-butene and ethylene-hexene copolymers, e.g., see Kaminsky et al, U.S. Pat. No. 4,542,199 and Sinn et al, U.S. Pat. No. 4,404,344, the entire contents of both of which are incorporated herein by reference.
However, although such zirconium-based catalysts are very effective olefin polymerization catalysts, the aluminoxane cocatalysts are expensive and can be utilized efficiently only if the olefin polymerization reactions are carried out in aromatic solvents (usually in toluene). Accordingly, a need exists in the art for alternative activators for such zirconium-based catalysts.
It is therefore a primary object of the present invention to provide a zirconium-based olefin polymerization catalyst composition comprising a zirconium-based catalyst precursor and an activator comprising a mixture of two compounds.
Other objects of the invention will become apparent to those skilled in the art from the following description thereof.